It doesn't really take a lot of intuition to know that the vast majority of startups are going to fizzle. Heck, "fail fast" is a mantra of the startup scene. Landlords just "know it" because they've already gone through it.

I think that the shared office spaces are really a wonderful solution so that young companies can have a great space without the long-term commitment. Ironically when we visited one (in Chicago) there were quite a few corporate "outposts" there with large companies like IBM.